System and Method for Terminal-Group Based HARQ for Cellular Integrated D2D Communications

ABSTRACT

System and method embodiments are provided to support network communications with groups of UEs. The embodiments include a two-level group-based hybrid-automatic repeat request (HARQ) mechanism and acknowledgement (ACK)/negative ACK (NACK) feedback. An embodiment method includes receiving, at a UE within a virtual multi-point (ViMP) comprising UEs, a data packet for a target UE (TUE) that is broadcasted from a base station (BS) to the ViMP node, decode the data packet, and upon successfully decoding the data packet, broadcasting the data packet to the UEs within the ViMP node until a timer pre-established by the BS expires or an ACK message is received from the TUE or the ViMP node. In an embodiment, broadcasted data received in the ViMP node is re-broadcasted upon receiving a negative acknowledgment (NACK) message from the TUE, a beacon UE, or any of the UEs within the ViMP node.

This application is a continuation of U.S. patent application Ser. No.13/829,188 filed on Mar. 14, 2013 by Amine Maaref et al. and entitled“System and Method for Terminal-Group Based HARQ for Cellular IntegratedD2D Communications,” which claims the benefit of U.S. ProvisionalApplication No. 61/738,907 filed on Dec. 18, 2012 by Amine Maaref et al.and entitled “System and Method for Network Coding AssistedTerminal-Group Based HARQ,” all of which applications are herebyincorporated herein by reference as if reproduced in their entirety.

TECHNICAL FIELD

The present invention relates to the field of wireless communications,and, in particular embodiments, to a system and method forterminal-group based HARQ for cellular integrated device-to-device (D2D)communications.

BACKGROUND

Direct mobile communications (DMC) and cellular controlled device todevice (D2D) communications are expected to play a significant role innext generation wireless networks. User equipment (UE) cooperation basedon D2D communications is one technology that is receiving attention.With advances in D2D communications, UE cooperation is expected to playa role in the future of wireless communications. This technology can beused to provide diversity in space, time and frequency, and increase therobustness against fading and interference. In UE cooperation, the D2Dcommunications are used to establish joint UE reception, where some ofthe UEs act as relays for other UEs to improve system throughput andcoverage. However, joint UE reception using D2D communications can alsoincrease the complexity of the network communications, such as forhybrid-automatic repeat request (HARQ) signaling. The HARQ mechanism isa link adaptation technique that can improve communications (forerroneous data packets) in current wireless cellular networks. However,current implementations of HARQ do not take UE grouping into account anddo not efficiently exploit D2D UE cooperation capabilities. Therefore,there is a need for efficient schemes that leverage UE cooperation andD2D communications with the HARQ mechanism.

SUMMARY

In accordance with an embodiment, a method for supporting two-levelterminal-group based hybrid-automatic repeat request (HARQ) signalingincludes receiving, at a (UE) within a virtual multi-point (ViMP) nodeof UEs, a data packet for a target UE (TUE) that is broadcasted from abase station (BS) to the ViMP node, attempting to decode the datapacket, and upon successfully decoding the data packet, broadcasting thedata packet within the ViMP node until a timer pre-established by the BShas expired or an acknowledgement (ACK) message is received from the TUEor the ViMP node.

In another embodiment, a method for supporting two-level terminal-groupbased HARQ signaling includes receiving, at a UE within a ViMP node ofUEs, a data packet that is broadcasted from a BS to the ViMP node andintended for the UE, attempting to decode the data packet, and uponsuccessfully decoding the data packet, broadcasting an ACK messagewithin the ViMP node and to the BS.

In another embodiment, a method for supporting two-level terminal-groupbased HARQ signaling includes broadcasting, at a BS, a data packet for atarget UE (TUE) to a ViMP node comprising UEs including the TUE,initiating a timer with a pre-determined time limit upon broadcastingthe data packet, and re-broadcasting the data packet to the ViMP nodeupon the timer reaching the time limit absent of receiving an ACKmessage from the TUE.

In yet another embodiment, a UE supporting two-level terminal-groupbased HARQ signaling includes a processor and a computer readablestorage medium storing programming for execution by the processor. Theprogramming includes instructions to receive, within a ViMP nodecomprising multiple UEs, a data packet for a TUE that is broadcastedfrom a BS to the ViMP node, attempt to decode the data packet, and uponsuccessfully decoding the data packet, broadcast the data packet withinthe ViMP node until a timer pre-established by the BS has expired or anACK message is received from the TUE.

In another embodiment, a UE supporting two-level terminal-group basedHARQ signaling includes a processor and a computer readable storagemedium storing programming for execution by the processor. Theprogramming includes instructions to receive, within a ViMP nodecomprising multiple UEs, a data packet that is broadcasted from a BS tothe ViMP node and intended for the UE, attempt to decode the datapacket, and upon successfully decoding the data packet, broadcasting anACK message within the ViMP node and to the BS.

In another embodiment, a network component supporting two-levelterminal-group based HARQ signaling includes a processor and a computerreadable storage medium storing programming for execution by theprocessor. The programming includes instructions to broadcast a datapacket for a TUE to a ViMP node comprising UEs including the TUE,initiating a timer with a pre-determined time limit upon broadcastingthe data packet, and re-broadcasting the data packet to the ViMP nodeupon the timer reaching the time limit until receiving an ACK messagefrom the TUE.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates D2D communications with UE cooperation;

FIG. 2 illustrates a BS communicating with cooperating UEs;

FIG. 3 illustrates an embodiment of a cooperative HARQ mechanism;

FIG. 4 illustrates an embodiment of a two-level HARQ scheme with a timerand without NACK feedback;

FIG. 5 illustrates an embodiment of a two-level HARQ scheme with a timerand second-level NACK feedback;

FIG. 6 illustrates a UE time/frequency resource grid; and

FIG. 7 illustrates a processing system that can be used to implementvarious embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

FIG. 1 illustrates a system 100 for D2D communications with UEcooperation. A plurality of UEs cooperate to form a logical/virtualmulti-point (ViMP) node 130 acting as single distributed virtualtransceiver. The term ViMP node can also be referred to herein as a UEgroup, cooperating UEs, or a joint reception/transmission group. A ViMPnode 130 includes a set of target UEs (TUEs) 120 and cooperating UEs(CUEs) 125. The CUEs 125 help the TUEs 120 communicate with a wirelessnetwork (not shown), e.g., to receive data on the downlink and/ortransmit data on the uplink. As such, the UEs of the ViMP node 130 canjointly transmit data on the uplink channel and jointly receive data onthe downlink channel.

Downlink ViMP reception involves two stages. In the downlink broadcastphase, the network broadcasts a data packet to the ViMP receiver (Rx)node 130 using ViMP-radio network temporary identifier (RNTI). Dependingon the ViMP cooperation scenario (e.g., capacity enhancement, coverageextension, or other scenarios), both TUEs 120 and CUEs 125 listen andtry to decode the data packet during this phase. In the D2D dataforwarding phase, the CUEs 125 forward some information to the TUEs 120to help them decode the information broadcast by the network during thefirst phase. Information sent by the CUEs 125 during this phase dependson the ViMP cooperation strategy (e.g., decode-and-forward (DF),amplify-and-forward (AF), joint reception (JR), or other strategies).

FIG. 2 illustrates a system 200 for a base station (BS) communicatingwith cooperating UEs. A BS 210 communicates in a downlink with a ViMP Rxnode 230 that includes a TUE 220 and one or more CUEs 225 (only one isshown), within a coverage range or cell range 240 of the BS 210.Depending on the DF relaying protocol, the whole codeword is decoded bythe CUE 225 before forwarding the whole or part of the message. If theCUE 225 cannot successfully decode a packet, the CUE 225 can still helpby cooperatively sending subsets of their log-likelihood ratios (LLRs).

Currently, the HARQ mechanism does not take UE grouping, such as insystems 100 and 200, into account and hence cannot efficiently takeadvantage of the D2D UE cooperation capabilities. System and methodembodiments are provided to support network (or BS) communications withgroups of UEs (e.g., in ViMP nodes). The embodiments include enhancedgroup-based retransmission mechanisms, e.g., a group-based HARQ scheme,and advanced ACK/NACK protocols, as described below.

In an embodiment for terminal-group based HARQ for cellular integratedD2D communications, a two-level HARQ mechanism is implemented to exploitthe group nature of the virtual multi-point (ViMP) transceiver (alsoreferred to herein as a terminal-group transceiver) to enable efficientretransmission of erroneous data packets in a D2D-enabled wirelesscellular network. Examples of cellular networks with D2D capabilityinclude but are not limited to 3GPP LTE, LTE-A, IEEE WiMAX, and similarsystems. The two-level terminal group-based HARQ mechanism also exploitsthe broadcast nature of the wireless channel. The second level of themechanism includes a distributed HARQ scheme that provides low signalingoverhead. The mechanism assisted by network coding, which reduces thenumber of required retransmissions, provides more efficient HARQ, andimproves throughput.

FIG. 3 illustrates an embodiment of a terminal-group based orcooperative HARQ mechanism 300. A group 315 of one or more BS 310 in thenetwork sends N packets p₁, p₂, . . . , p_(N) (N is an integer) to aplurality of TUEs 325 in a ViMP node 330. The packets can be sentsequentially over time during N broadcast phases, e.g., if there is asingle TUE 320 in the ViMP node 330. Less than N broadcast phases may beused if there are multiple TUEs 320 in the ViMP node 330 or in case ofUEs supporting multi-rank transmissions. Each packet is controlled by aseparate HARQ process. During each broadcast phase, the TUE 320 and allthe involved CUEs 325 try to decode. During the data forwarding phase,the CUEs 325 forward to the TUEs 320 a network coded version of: (i) thesame original packets they have successfully decoded (e.g. p=p₁⊕p₂⊕ . .. ⊕p_(N)), (ii) additional coded symbols in case of a concatenatedlow-density parity-check (LDPC) coding scheme for half-duplexdecode-and-forward (DF) relays, and/or (iii) a given redundancy version,e.g., using Turbo-Coding. Based on the soft information that the TUE(s)320 receive for p₁, p₂, . . . , p_(N) from a BS 310 or the group 315 andthe additional information forwarded by the CUEs 325, the TUE(s) 320 tryto decode their own packets. If a TUE 320 is able to decode a packet, itbroadcasts an acknowledgement (ACK) message within the ViMP node 330 andback to the BS 310 or the group 315.

The network coded packet transmitted by each CUE 325 is not necessarilybased on an XOR operation, which corresponds to operation in a GalloisField of order 2, GF(2). An operation in any GF(2^(n)) where n>1 is alsopossible, in which case the network coded packet may consist of anylinear combination of the successfully decoded packets according to:

p=α ₁ p ₁+α₂ p ₂+ . . . +α_(N) p _(N),

where α₁, α₂, . . . , α_(N) are coefficients that are sent to the TUE320 along with the information on which packets were network coded. Inanother embodiment, the coefficients α₁, α₂, . . . , α_(N) can be knownbeforehand and do not need to be forwarded by the CUEs 325.

FIG. 4 illustrates en embodiment of a two-level HARQ scheme 400 withoutNACK feedback, which can be used in the HARQ mechanism 300. At a firstlevel of the HARQ scheme 400 between an eNB (or a BS) and a ViMP node(or UE group), the eNB sends a packet to the UE group, and a timer isstarted at the eNB. While the timer <T₀ (T₀ is a pre-determined timelimit), the TUE and CUEs within the ViMP node try to decode the packet,and the CUEs which successfully decode the packet broadcast the packetwithin ViMP node. At a second level of the HARQ scheme 400 within theViMP node, the CUEs that can decode the packet, either from the firsteNB transmission or from a broadcast by other CUEs, broadcast the packet(or another version) within the ViMP node. The second level HARQ processwithin the ViMP Rx node continues until the packet is successfullydecoded by the TUE. In this case, an ACK is broadcast within the ViMPnode and sent back to the eNB. Otherwise, the second level HARQ processwithin the ViMP Rx node continues until the timer at the eNB reaches thelimit T₀. In this case, the eNB assumes a Negative ACK (NACK) responseand resends the packet (or another version). In the scheme 400, the TUEdoes not actually transmit a NACK response if the packet is notsuccessfully decoded. The second level distributed HARQ uses theparticipation of UEs within the ViMP node without synchronization withthe eNB (or the network) and without using scheduling within the ViMPnode.

FIG. 5 illustrates an embodiment of a two-level HARQ scheme 500 withNACK feedback within a ViMP node, which can be used in the HARQmechanism 300. At a first level of the HARQ scheme 500, a eNB (or BS)sends a packet to a ViMP node (or UE group), and a timer is started atthe eNB. While the timer <T₀, the TUE and CUEs within the ViMP node tryto decode the packet, and the CUEs that successfully decode the packetsend a broadcast packet within ViMP node. At the second level HARQwithin the ViMP node, if the packet is not successfully decoded by theTUE, then the TUE broadcasts a NACK message within the ViMP Rx node.Thus, the CUEs that can decode the packet, either from the first eNBtransmission or from a broadcast by other CUEs, broadcast the packet oranother version within the ViMP node. The second level HARQ processwithin the ViMP Rx node continues until the packet is successfullydecoded by the TUE. In this case, an ACK is broadcast within the ViMPnode and sent to the eNB. Otherwise, the second level HARQ processwithin the ViMP Rx node continues until the timer at the eNB reaches alimit. In this case, the eNB assumes a NACK and resends the packet oranother version. In the scheme 500, the CUEs rebroadcast the packet atthe second level HARQ within the ViMP node if or upon receiving the NACKfrom the TUE. The second level distributed HARQ uses the participationof UEs within the ViMP node without synchronization with the eNB (or thenetwork) and without using scheduling within the ViMP node.

FIG. 6 illustrates a time/frequency resource grid 600 from all UEs 620(including TUEs and CUEs) in a ViMP node. For decoding at a TUE,transmissions from different CUEs are separated in thetime/frequency/code domain (or any combinations thereof) to distinguishbetween them at the TUE. In one embodiment, different HARQ redundancyversions/LDPC codewords are mapped to orthogonal signatures and sentfrom different CUEs. The TUE accumulates the soft information receivedfrom all CUEs along with the information that the TUE received from theBS to try to decode the packets.

The target UE can be declared in different levels explicitly orimplicitly in the control channel, where the target UE is known to thegroup, or explicitly or implicitly in the data packet, where the targetUE is only known after the data is correctly decoded. With a cleartarget UE at control channel, the target UE may send a NACK if it doesnot receive the packet. Without a clear target UE at control channel,the system may lack an explicit NACK signaling. The NACK may beimplicitly implied when no ACK is received.

The ACK/NACK signaling to the network can be sent by the TUE or the CUE.It can be done proactively (by any UE in the group receiving it) orreactively by the TUE only. Proactively, each UE in the group, whichreceives the data, sends back an ACK and takes responsibility for dataforwarding. A NACK may be in this case implied by not sending an ACKmessage. If more than one UE receives the data, the ACK signal from theUEs may be combined over the air. A beacon UE is a UE in the group(probably with the best channel and not necessarily the TUE) that takescare of the ACK channel. Reactively, the TUE sends ACK/NACK after itreceives help from other UEs considering the process and forwardingtime.

FIG. 7 is a block diagram of a processing system 700 that can be used toimplement various embodiments. Specific devices may utilize all of thecomponents shown, or only a subset of the components, and levels ofintegration may vary from device to device. Furthermore, a device maycontain multiple instances of a component, such as multiple processingunits, processors, memories, transmitters, receivers, etc. Theprocessing system 700 may comprise a processing unit 701 equipped withone or more input/output devices, such as a speaker, microphone, mouse,touchscreen, keypad, keyboard, printer, display, and the like. Theprocessing unit 701 may include a central processing unit (CPU) 710, amemory 720, a mass storage device 730, a video adapter 740, and an I/Ointerface 750 connected to a bus. The bus may be one or more of any typeof several bus architectures including a memory bus or memorycontroller, a peripheral bus, a video bus, or the like.

The CPU 710 may comprise any type of electronic data processor. Thememory 720 may comprise any type of system memory such as static randomaccess memory (SRAM), dynamic random access memory (DRAM), synchronousDRAM (SDRAM), read-only memory (ROM), a combination thereof, or thelike. In an embodiment, the memory 720 may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms. The mass storage device 730 may comprise any type of storagedevice configured to store data, programs, and other information and tomake the data, programs, and other information accessible via the bus.The mass storage device 730 may comprise, for example, one or more of asolid state drive, hard disk drive, a magnetic disk drive, an opticaldisk drive, or the like.

The video adapter 740 and the I/O interface 760 provide interfaces tocouple external input and output devices to the processing unit. Asillustrated, examples of input and output devices include a display 760coupled to the video adapter 740 and any combination ofmouse/keyboard/printer 770 coupled to the I/O interface 760. Otherdevices may be coupled to the processing unit 701, and additional orfewer interface cards may be utilized. For example, a serial interfacecard (not shown) may be used to provide a serial interface for aprinter.

The processing unit 701 also includes one or more network interfaces750, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or one or more networks 780.The network interface 750 allows the processing unit 701 to communicatewith remote units via the networks 780. For example, the networkinterface 750 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing unit 701 is coupled to alocal-area network or a wide-area network for data processing andcommunications with remote devices, such as other processing units, theInternet, remote storage facilities, or the like.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method for supporting two-level terminal-groupbased hybrid-automatic repeat request (HARM) signaling, the methodcomprising: receiving, at a cooperating user equipment (CUE) within avirtual multi-point (ViMP) node comprising a plurality of UEs, a datapacket for a target UE (TUE) that is broadcasted from a base station(BS) to the ViMP node; successfully decoding the data packet; withoutreceiving an acknowledgement (ACK) message or a negative ACK (NACK)message from the TUE, broadcasting, by the CUE, the data packet withinthe ViMP node; and without receiving a negative acknowledgement (NACK)message from the TUE, rebroadcasting, by the CUE, the data packet withinthe ViMP node until either the CUE receives another broadcast of thedata packet from the BS, or the CUE receives an acknowledgement (ACK)message from the TUE or the ViMP node.
 2. The method of claim 1 furthercomprising: receiving the broadcasted data packet from one or more UEsin the ViMP node; and wherein the rebroadcasting comprisesrebroadcasting within the ViMP node the broadcasted data packet or thedata packet initially received from the BS.
 3. The method of claim 2,wherein the data packet is rebroadcasted within the ViMP node until theCUE receives the another broadcast of the data packet from the BS. 4.The method of claim 2, wherein the data packet is re-broadcasted untilthe ACK message is received from the TUE, a beacon UE, or any of the UEsin the ViMP node.
 5. The method of claim 1 further comprising receivingthe another broadcast of the data packet from the BS in response to atimer pre-established by the BS expiring.
 6. The method of claim 1,wherein the data packet is rebroadcasted within the ViMP node withoutscheduling of the UEs within the ViMP node and without synchronizationwith the BS.
 7. The method of claim 1, wherein the data packetrebroadcasted to the UEs in the ViMP node comprises a network codedversion of the same received and decoded data packet, additional codedsymbols in case of a concatenated low-density parity check (LDPC)coding, or a given redundancy version in case of turbo coding.
 8. Themethod of claim 7, wherein the network coded version comprises a linearcombination of successfully decoded packets, and wherein the decodedpackets are combined using coefficients that are sent to the TUE withinformation on which packets were network coded.
 9. The method of claim7, wherein the network coded version comprises a linear combination ofsuccessfully decoded packets, and wherein the decoded packets arecombined using coefficients that are known beforehand by the TUE. 10.The method of claim 1 further comprising: receiving, from the BS, datapackets with different HARQ redundancy versions, low-density paritycheck (LDPC) codewords, or both for different TUEs, wherein thedifferent HARQ redundancy versions and LDPC codewords are mapped toorthogonal signatures; and rebroadcasting the data packets to the UEs inthe ViMP node.
 11. A method for supporting two-level terminal-groupbased hybrid-automatic repeat request (HARQ) signaling, the methodcomprising: receiving, at a cooperating user equipment (CUE) within avirtual multi-point (ViMP) node comprising a plurality of UEs, a datapacket for a target UE (TUE) that is broadcasted from a base station(BS) to the ViMP node; successfully decoding the data packet; withoutreceiving an acknowledgement (ACK) message or a negative ACK (NACK)message from the TUE, broadcasting, by the CUE, the data packet withinthe ViMP node; receiving, by the CUE, the NACK message from the TUE;rebroadcasting, by the CUE, the data packet within the ViMP node inresponse to receiving the NACK message; and receiving either anotherbroadcast of the data packet from the BS or an ACK message from the TUE.12. The method of claim 11 further comprising: receiving the broadcasteddata packet from one or more UEs in the ViMP node; and wherein therebroadcasting comprises rebroadcasting within the ViMP node thebroadcasted data packet or the data packet initially received from theBS.
 13. The method of claim 12, wherein the data packet is rebroadcastedwithin the ViMP node until the CUE receives the another broadcast of thedata packet from the BS.
 14. The method of claim 12, wherein the datapacket is rebroadcasted until the ACK message is received from the TUE.15. The method of claim 11 further comprising receiving the anotherbroadcast of the data packet from the BS in response to a timerpre-established by the BS expiring.
 16. The method of claim 11, whereinthe data packet is rebroadcasted within the ViMP node without schedulingof the UEs within the ViMP node and without synchronization with the BS.17. The method of claim 11, wherein the data packet rebroadcasted withinthe ViMP node comprises a network coded version of the same received anddecoded data packet, additional coded symbols in case of a concatenatedlow-density parity check (LDPC) coding, or a given redundancy version incase of turbo coding.
 18. The method of claim 17, wherein the networkcoded version comprises a linear combination of successfully decodedpackets, and wherein the decoded packets are combined using coefficientsthat are sent to the TUE with information on which packets were networkcoded.
 19. The method of claim 17, wherein the network coded versioncomprises a linear combination of successfully decoded packets, andwherein the decoded packets are combined using coefficients that areknown beforehand by the TUE.
 20. The method of claim 11 furthercomprising: receiving, from the BS, data packets with different HARQredundancy versions, low-density parity check (LDPC) codewords, or bothfor different TUEs, wherein the different HARQ redundancy versions andLDPC codewords are mapped to orthogonal signatures; and rebroadcastingthe data packets to the UEs in the ViMP node.